Field of the Invention
The invention relates to a semiconductor module having an electrically insulating and thermally conductive substrate being connected in material-locking fashion to the top of a metal base plate, and semiconductor chips being connected in material-locking fashion to the top of the substrate, the underside of the base plate being constructed to be convex.
One such semiconductor module has been described in German Published, Non-Prosecuted Application DE 39 40 933 A1, for instance. The base plate therein is made convex, in order to enable satisfactory thermal contact between it and a cooling body during semiconductor module operation as well. The base plate, which is shaped to be convex with respect to the cooling body, is screwed on its ends to the cooling body. The base plate thus rests with its entire surface against the cooling body. The convex deformation is chosen to be so great that during operation the base plate does not arch upward in the middle.
In the module described in the aforementioned prior art, the base plate is of equal thickness over its entire surface. A convex deformation relative to the cooling body therefore causes a concave deformation on the top or upper surface. Since the substrate is joined to the base plate and the semiconductor chips are joined to the substrate usually by soft soldering, the molten solder has the tendency to flow away. That makes simple assembly of both the substrate and the semiconductor chips by simple solder preforming impossible. Thus the greater the convexity of the base plate and the more parts that have to be mounted on the base plate, the more difficult simple assembly becomes.